1. Field of the Invention
The preferred embodiments of the present invention relate, inter alia, to a friction clutch and a vehicle equipped with the friction clutch.
2. Description of the Related Art
Vehicles equipped with a friction clutch for connecting and disconnecting engine power transmission and a clutch operator for operating the friction clutch are conventionally known. For example, motorcycles are provided with a clutch lever as the clutch operator.
Generally, as a vehicle increases in size, the friction clutch will increase in capacity correspondingly, and the force required for disengaging the friction clutch will increase accordingly. As a consequence, the driver's burden in clutch operation increases. In order to reduce the rider's burden in clutch operation, it has been proposed to add the so-called operation assist mechanism to the friction clutch (for example, see JP S52-004955 A (hereinafter referred to as “Patent Document 1”) and Japanese Patent No. 3381442 (hereinafter referred to as “Patent Document 2”)).
The friction clutch having an operation assist mechanism described in Patent Document 1 is provided with a drive-side rotating member having a power-transmitting-side plate, a driven-side rotating member having a power-transmitted-side plate, and a pressure plate for bringing the power-transmission-side plate and the power-transmitted-side plate into pressure contact with each other by receiving an urging force from a pressure-contact spring. This friction clutch has an operation assist mechanism comprising a pressing member that integrally rotates together with the driven-side rotating member, a torque transmission member that faces the pressing member across the friction plate, and a ball cam that moves the pressure plate in a direction in which the power-transmission-side plate and the power-transmitted-side plate separate from each other when the torque transmission member receives torque. The friction clutch also is equipped with an operating shaft for moving the pressing member toward the torque transmission member at the time of disengaging the clutch, and a clutch operator that imparts a force for moving the pressing member toward the torque transmission member to the operating shaft.
In the friction clutch described in Patent Document 1, at the time of disengaging the clutch, the pressing member is pressed against the torque transmission member via the friction plate to impart torque from the pressing member to the torque transmission member. This enables the ball cam to move the pressure plate in the direction in which the power-transmitting-side plate and the power-transmitted-side plate separate from each other. Therefore, in this friction clutch, a part of the torque of the driven-side rotating member is utilized as the force for separating the power-transmitting-side plate and the power-transmitted-side plate away from each other. As a result, this friction clutch can reduce the force necessary for separating the power-transmitting-side plate and the power-transmitted-side plate away from each other. Note that in the following description, the member formed by the pressing member, the friction plate, and the torque transmission member will be referred to as a “sub-clutch.”
The force necessary for disengaging the clutch described above is a force exceeding the urging force of the pressure-contact spring, etc. Here, the force necessary for disengaging the clutch is denoted as an operating force P. In the friction clutch having an operation assist mechanism, the operating force P is the resultant force of a force input from the clutch operator (referred to as an “operation input,” denoted as “f1”), and a force with which the operation assist mechanism additionally gives for disengaging the clutch (referred to as an “assist force,” and denoted as “f2”). In other words, when the clutch is kept in a disengaged state, the equation P=f1+f2 is established between the operating force P, the assist force f2, and the operation input f1. The operation force P is a constant value. Here, the magnitude of the assist force depends on the magnitude of the friction force generated between the friction plate and the torque transmission member. On the other hand, the magnitude of the just-mentioned friction force depends on the magnitude of the force with which the pressing member presses the friction plate toward of the torque transmission member, i.e., the magnitude of the operation input. Thus, the magnitude of the assist force, after all, depends on the magnitude of the operation input. Accordingly, the relation between the assist force and the operation input is defined as an assist ratio A=f2/f1. Hence, the equation P=f1(1+A) is established between the operating force P, and the assist ratio A, and the operation input f1.
There is a demand for a reduction of f2 depending on the specifications of the vehicle equipped with the friction clutch, the operator who operates the friction clutch, or the like. For example, there may be a case in which reduction of the assist force is desired for the purpose of reducing the noise or vibration produced around the operation assist mechanism or adjusting of the clutch operating force.
However, the operation force P is represented as the equation P=f1+f2 and that the operating force P is a constant value as explained above, and therefore in the case of decreasing f2, f1 should be increased. However, the increased f1 increases the force with which the pressing member presses the torque transmission member via the friction plate. As a consequence, the friction forces produced between the pressing member and the friction plate and between the friction plate and the torque transmission member will increase, which in turn increases the load to the pressing member, the friction plate, and the torque transmission member. For this reason, merely reducing f2 poses a concern about the durability of the pressing member, the friction plate, and the torque transmission member.
On the other hand, in order to ensure the durability of the pressing member, the friction plate, and the torque transmission member, it can be considered, for example, to increase the sizes of the pressing member, the friction plate, and the torque transmission member to enhance their strength. This, however, results in an increase of the clutch in size.
The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present invention. For example, certain features of the preferred embodiments of the invention may be capable of overcoming certain disadvantages and/or providing certain advantages, such as, e.g., disadvantages and/or advantages discussed herein, while retaining some or all of the features, embodiments, methods, and apparatus disclosed therein.